As lawn care enters the summer months, two of the most common weeds likely to become a nuisance are crabgrass and perennial nutsedges. Like all weeds, successful long-term management strategies begin with a dense, healthy turfgrass.
However, factors such as disease, insects, improper mowing, low fertility, and drought can weaken or thin turfgrass. This is when weeds will take an opportunity to quickly infest a lawn and spread. Coupling proper cultural practices and timely herbicide applications are important for effective summer weed management.
Before herbicide applications are made, proper weed identification must be accomplished. Smooth crabgrass (Digitaria ischaemum) and large crabgrass (Digitaria sanguinalis) are two common crabgrass species found throughout cool- and warm-season turfgrass.
Crabgrass is a pale green-colored summer annual weed that disrupts the overall color and density of a dark, green lawn. Crabgrass can produce up to 150,000 seeds per plant, which may remain viable in the soil for several years. Crabgrass plants have pointed leaf tips with round stems and leaf blades typically longer than two inches. Both smooth and large crabgrass have tall, membranous ligules at the base of the leaf blade. Smooth crabgrass plants do not have hairs on the leaf sheath and will typically see a red to maroon color at the base. Large crabgrass plants have hairs on the leaf and sheath. Both species produce seed heads with “finger-like” spiked branches.
The two most common perennial nutsedge species that infest turfgrass are yellow (Cyperus esculentus) and purple (Cyperus rotundus) nutsedge. Nutsedge reproduce primarily by tubers, sometimes referred to as nutlets. Nutsedge can be spread from one location to another by planting infested sod or spreading soil containing viable tubers. Emergence will vary depending on geographic location and soil type.
Generally, these weeds can emerge as early as April and thrive throughout the summer months into the fall. Both have triangular shaped stems and a three-ranked leaf arrangement, which means one leaf is produced on each point of the triangle. Purple nutsedge will have a blunt leaf tip whereas yellow nutsedge will have a more tapered leaf tip. One of the most common ways to distinguish yellow from purple nutsedge is the color of the seed head. Yellow nutsedge has golden-colored seed heads arranged in a cluster of spikelets. Purple nutsedge produces maroon to purple seed heads arranged similarly.
Control of annual weeds like crabgrass begins with preemergence applications in spring. There may be seasons when preemergence herbicide applications are unable to be made on time due to unforeseen circumstances, which will warrant postemergence herbicide applications in summer. There are a few essential factors in applying postemergence herbicides to maximize effective crabgrass and nutsedge control.
Application Timing – In general, weeds are more susceptible to postemergence herbicides during the early growth stages of development. As a weed grows, it can be more difficult to control. Depending upon the herbicide used, better crabgrass control can be achieved when targeting the leaf stage to early tiller stage as compared to larger plants. Sequential applications may be needed to control larger crabgrass plants. For nutsedge, applications should be applied prior to new tuber development. This typically coincides with early growth stages when soil temperatures are between 65 and 70°F.
Application Technique – Proper coverage is needed for postemergence herbicide applications. Nozzle size and spray volume are important to ensure the target weed receives the proper herbicide rate. Larger droplet sizes or poor spray volume may result in a lack of control. This is particularly important when managing weeds like nutsedge where the leaf blade is upright and has a high amount of cuticular wax. If using a backpack sprayer, a flat fan nozzle would be the preferred nozzle type. In some cases, applicators make more than one swath, or apply in circular pattern over the target area. This spray pattern can increase the use rate and potentially cause unwanted turfgrass discoloration. It is important to apply the herbicide evenly across patches moving from one direction to the next (i.e., left to right).
Created in partnership with the experts at FMC True Champions.